The current invention is generally related to detecting a character based upon character edges, and more particularly related to a method and a system for determining character edges based upon certain predetermined conditions of edge pairs as units.
In order to detect edges in text or characters, certain image characteristics are utilized. For example, the certain image characteristics include a local change in intensity as well as the continuous intensity level in the image. Another exemplary image characteristics is the symmetry in intensity change. Based upon these and other image characteristics, prior attempts have disclosed various method in discriminating character edges.
Hei 3-64251 discloses a system that detects a local edge and further processes the local edge by eliminating a false character edge based upon the screen dots detection. The screen dots is defined to be a symetrical non-character edge. Although some screen dots are eliminated, since only local edges are considered for determining character edges, some false character edges are erroneously included.
Hei 6-150059 discloses a system that correctly discriminates chekered patterns and dense-line area as characters based upon a combination of a predetermined edge pattern detection, a net pattern detection, and a line orientation pattern detection. Unfortunately, since this prior attempt requires a predetermined set of fixed patterns to detect character edges, the character edge recognition is limited by the available fixed patterns.
Hei 7-95397 discloses a system for correcting the between-edge signal based upon the size or the thickness of an input character. To select character edges, the edges are detected based upon pattern matching to eliminate xe2x80x9cscreen dots.xe2x80x9d The improved process includes that the logical AND process based upon the selected character candidate areas marked by character edges and an on/off signal. The image resolution is generally degraded in the middle portion of a thick-lined character between its edges due to a simple binarization. Although there is some improvement on the binarization results, when the on/off signal is near a threshold value, the logical AND gate undesirably outputs a mixture of on and off outputs.
Hei 5-145749 discloses a system for improving the binarization process by performing simple binarization from an onset of detecting a starting-edge beyond a first predetermined threshold to another onset of detecting an ending-edge below a second predetermined threshold. Although this improved process prevents the degraded middle portion of a thick lined character between its edges, since the improved process relies upon the detection of the starting-edges and the starting edges include both character as well as non-character edges, the accuracy remains to be desired.
In view of the above described prior attempts, it is desired that edges are detected only for characters based upon certain predetermined conditions that are applicable to most characters.
In order to solve the above and other problems, according to a first aspect of the current invention, a method of detecting character edges, includes inputting image data; detecting a first edge point in the image data; detecting a second edge point which corresponds to the first edge point, the first edge point and the second edge point defining an edge pair; detecting a change in pixel value within the edge pair; and determining whether or not the edge pair as a unit is a character portion based upon the change in the pixel value between the edge pair with respect to a predetermined set of conditions for defining the character portions.
According to a second aspect of the current invention, a system for detecting character edges, including: an image input unit for inputting image data; an edge detection unit connected to the image unit for detecting a first edge point in the image data, the edge detection unit also detecting a second edge point which corresponds to the first edge point, the first edge point and the second edge point defining an edge pair; and an edge pair evaluation unit connected to the edge detection unit for detecting a change in pixel value within the edge pair, the edge pair evaluation unit determining whether or not the edge pair as a unit is a character portion based upon the change in the pixel value between the edge pair with respect to a predetermined set of conditions for defining the character portions.